1. Field of the Invention
The present invention relates to a printed circuit board positioning apparatus incorporated in an automatic electronic parts mounting machine and, more particularly, to a printed circuit board positioning apparatus which can smoothly position a printed circuit board before electronic parts are mounted thereon.
2. Description of the Prior Art
In a typical conventional printed circuit board positioning apparatus of this type which is incorporated in an automatic electronic parts mounting machine, a guide hole is formed in a printed circuit board surface to serve as a positioning reference, and a guide pin is inserted in the guide hole to accurately position the printed circuit board.
However, in such a conventional printed circuit board positioning apparatus, in order to smoothly insert/remove the guide pin into/from the guide hole formed in the printed circuit board surface, the guide hole is formed to be a circular hole or an elongated hole having a diameter slightly larger than that of the guide pin and hence has a margin. Therefore, during positioning of the circuit board, an insertion position of the guide pin tends to offset from a proper position by an amount of the margin of the guide hole in the printed circuit board, thereby producing an error in positioning of the printed circuit board.
In order to eliminate the above drawback of the conventional apparatus, a printed circuit board positioning apparatus has been proposed as disclosed in Japanese Patent Laid Open (Kokai) No. 59-29493 which is already applied and disclosed in Japan.
In the printed circuit board positioning apparatus disclosed in the above Japanese Patent Disclosure, a pair of circuit board transporting chutes are provided on a table which can be moved in an X-Y direction so that the circuit board transporting chutes oppose each other through a chute support base which can be moved upward/downward. Both end faces in the widthwise direction of the printed circuit board are inserted and held between the pair of circuit board transporting chutes, and one of the circuit board transporting chutes is allowed to move in the widthwise direction of the printed circuit board and elastically urged by an urging means. At the same time, a guide pin extending from the table is inserted in a guide hole of the printed circuit board by downward movement of the circuit board transporting chutes which are moved downward together with the chute support base. Thereafter, one end face in the longitudinal direction of the printed circuit board is elastically urged by a circuit board urging pivoting lever, so that the guide pin is kept urged against a peripheral portion of the guide hole of the printed circuit board. As a result, relative offset between the guide hole of the printed circuit board and the guide pin is prevented, and the printed circuit board can be accurately positioned.
However, when positioning is performed on the basis of end faces of the printed circuit board in a direction perpendicular to a flowing direction thereof and engagement between the guide hole of the printed circuit board and the guide pin, a high packing density of electronic parts to be mounted on the printed circuit board surface is prevented especially because the guide hole for positioning is formed in the printed circuit board surface.
In an apparatus wherein the rear surface of the printed circuit board can be supported by backup pins extending from the table at a predetermined low position of the circuit board transporting chutes which are moved downward together with the chute support base, a position of the printed circuit board in the flowing direction thereof is adjusted on the basis of a contact state between the printed circuit board and the backup pins. In this case, since a friction resistance is produced between the printed circuit board and the backup pins, a large urging force is required for the circuit board urging pivoting lever to elastically urge one end face of the printed circuit board in its flowing direction. In addition, not only the rear surface of the printed circuit board tends to be damaged but also the backup pins are abraded by frequent use over a long period of time. As a result, an error is produced in positioning precision also in the vertical direction of the printed circuit board.